This invention concerns improvements in and relating to monitoring emissions, and in particular, but not exclusively to the monitoring of positions and/or levels and/or changes in emissions from radioactive sources.
Alpha particles, for instance, are emitted from a variety of radioactive sources. The determination of the presence, level and position of alpha emitting sources is important in many applications, including decommissioning. Alpha particles only travel a few centimetres in air and as a consequence their direct detection at any great distance is not possible.
Some existing instruments, for alpha emission monitoring, generally call for the instrument to be placed in close proximity to the surface to be measured. This can be difficult for some surfaces and is time consuming when any significant size of area is under consideration.
Alternative instruments, for alpha emission monitoring, require a flow of air from in proximity with the source(s) to a detection unit, where ions produced by the alpha particles are measured. This type of system is restricted to situations in which a controlled flow path can be provided. The distance over which this type of remote monitoring can be provided is also restricted.
Monitoring of other emissions, such as beta particles, gamma rays, neutrons, fission fragments, positrons and n-alpha""s, also face problems. In many cases the distances over which monitoring can be effected are limited and physical access to the source is required.
Problems also occur with monitoring as the environment under consideration is likely to have an ambient light level and/or may be heavily shielded relative to locations from which monitoring can be performed.
The present invention aims to provide a method of, and apparatus for, monitoring emissions successfully, particularly with a view to determining their location and/or level and/or to determine changes in emissions. This monitoring may be achieved from a significant distance from the emission source.
According to a first aspect of the invention we provide a method of monitoring emissions from one or more radioactive sources in an area, comprising the steps of presenting photon detecting means to the area to be monitored, the photon detecting means producing a signal indicative of photons detected, the signal being processed to produce an indication of the emissions from the radioactive source.
The emissions may arise from one or more sources. The sources may occur discreetly or as a non-discrete mass. Alpha emitting sources may include plutonium, uranium, americium and the like. Beta and/or gamma emitting sources may include caesium-137 and cobalt-60. Sources may also include materials or locations which give out emissions in response to an input, for instance an interrogating beam of neutrons. The source may not emit in the absence of the input. The emissions may give an indication of the presence of and/or position of and/or level of fissile material and/or the presence of and/or position of and/or the level material which can react by the (n,xcex1) mechanism, such as boron or lithium at the location in such a case.
The photons preferably arise from scintillation caused by the emissions. The scintillation is preferably caused by the electronic de-excitation of atoms and/or molecules and/or ions within the environment from an elevated energy level to a lower energy level. Preferably the elevated energy level is caused by the passage of alpha particles and/or beta particles and/or gamma rays and/or fission fragments and the like.
The photon detecting means may be presented to the area by moving the detecting means.
The detecting means may be moved by changing the position of the unit on which they are provided. The unit may be moved by advancing the unit over a surface of the environment in which the unit is provided. The moveable unit may be remote controlled, for instance in terms of its position.
The detecting means may be moved by altering the angle of inclination of the detecting means relative to the horizontal and/or by altering the angular position of the detecting means about the vertical. The detecting means may be moved by a pan and tilt style mounting. The detector means may be remotely controlled, for instance in terms of its inclination or angular position.
The detecting means may be hand-held and/or may be moved by the hand of the operator.
The photon detecting means may be presented to the area by moving the area relative to the detecting means. The area may be provided on a moving belt or other form of transport means. The transport means may be used to move item(s) and/or material to be monitored past the detecting means, thereby presenting different areas to the detecting means.
The detecting means may be provided at a location to which discrete items are introduced and removed. The detecting means may be provided in one configuration to allow access to the location and a different configuration to allow monitoring. The detecting means may enclose the location during monitoring. The detecting means may be partially removed to allow access to the location.
The detecting means may be provided in a fixed position relative to the area. The detecting means may be provided above the area to be monitored.
The detector means may be presented to the area at a location remote from the area, photons being conveyed to the remote location. The photons may be conveyed by fibre optics.
The photons detected may consist of those travelling directly from the place of scintillation to the detector means. A method of, or means for, directing other photons to the detecting means may be provided. Mirrors, including planar and/or focussing mirrors may be provided to reflect other photons to the detector means.
The area to be monitored may be or be a portion of an environment. The area may overlap with other areas previously or subsequently monitored by the same method by the same instrument. The area may overlap with areas previously, simultaneously or subsequently monitored by one or more other instruments applying the same method.
The method may include scanning, for instance by moving the detecting means, so as to monitor a plurality of areas within the environment. Scanning may be provided by moving means for conveying photons to the detecting means, for instance the fibre optics. The detecting means may remain in a fixed position during such a scan. The fibre optics or a portion thereof may be moveable, preferably in a controlled manner such as that provided by an endoscope.
The photons may pass through a shield transparent to at least a part of the wavelengths of the photons prior to reaching the detecting means. The shield may block the passage of radiation, or at least a significant portion thereof.
The whole of an environment may be monitored from a single position and/or a number of different positions.
The photon may be detected by a light sensitive device such as photomultiplier, and most preferably an ultra violet light sensitive device and/or a solar blind photomultiplier. The light sensitive device may be collimated.
The photons to be detected and/or the photons to be considered may be selected from one or more emitted wavelengths or ranges thereof. The wavelengths detected and/or considered may be below 400 nm, more preferably below 350 nm and ideally below 325 nm. The range of wavelengths detected and/or considered may be indicative of scintillation from a particular component of the environment around the area, for instance nitrogen in the air around the surface carrying the source. The range of wavelengths may represent only some of the scintillations from that component. The selected range of wavelengths may be 220 to 320 for nitrogen. Preferably the selected waveband is one not containing a significant number of photons arising from the ambient light conditions for the area. The ambient light may be daylight and/or artificial light.
Ambient light may substantially or completely be excluded from the area. The instrument and/or light shields may be used to exclude ambient light from the area.
An environment may be a room, tank, vessel, cell, container, glove box, pipe, duct or the like. The interior and/or exterior surfaces may be investigated. The area may comprise the whole of an environment, such as in the case of the interior of a pipe, or may comprise a portion thereof, such as a floor, part of a floor or the like.
An area may be defined as the field of view of the detecting means. The field of view may be defined as the space in which scintillating sources will be observed. The field of view may be a cone shaped space, parabolic cone or Fresnel screen. The apex angle of the cone may be defined by the collimation of the photon detecting means.
The signal preferably includes information directly related to the number of photons detected.
The signal may include information from a range finder about the distance between the detector and one or more locations within the environment, particularly within the field of view of the detector.
The signal may be conveyed to the processing directly, for instance through wire(s), or may be relayed indirectly, for instance as a radio signal.
The processing preferably converts the detected photons into an indication of emissions. The processing may equate or calculate the emission level from pre-determined information about level as a function of photons detected, and particularly the level of photons detected. The indication of emissions may relate to the type of source causing the emissions. The processing may provide a level of alpha emissions and/or beta emissions and/or gamma emissions and/or other emission types singularly and/or may provide a level of overall emissions.
The processing may involve the subtraction of background scintillation from the signal. A second detecting means, receiving background only scintillations, may be used to provide the subtraction signal.
The processing may generate positional information about the source of the signals, for instance three dimensional co-ordinates for the field of view may be generated from the two angle and range signals for the detecting means.
The indication, for instance of the alpha emissions, may include one or more of, the total emission level, the emission level of distinct sources and/or areas, the direction of the emission source(s), the distance of the emission source(s) from the detector(s), the position of the emission source(s) relative to the detector(s) and/or relative to the environment the source(s) is in, such as the boundaries of a room.
The indication may express the level of one or more, and preferably each, discrete source found within the environment monitored or areas thereof. The indication may express the overall contamination level of the environment monitored or areas thereof.
The position may be expressed as three-dimensional co-ordinates relative to the environment the source(s) are in. The co-ordinates may be referenced relative to a corner of the environment, such as a corner between floor and two walls. The position may be expressed as an angle, more preferably 2 angles, relative to the detector and a distance between the detector and the source(s).
Positional and level information may be combined in the indication. The indication may comprise one or more 2-D slices or views and/or 3-D representations of the environment or areas thereof together with level indications. Contour plots of the contamination may be provided.
The emission information may be overlaid on a visual image of the area, the areas environment or both. The visual image may be taken from close to the detector means viewpoint.
According to a second aspect of the invention we provide an emission monitoring instrument comprising photon detection means and processing means, the photon detecting means producing a signal in response to photons, the processing means acting on the signal to give an indication relating to the emissions.
The photons preferably arise from scintillation caused by the passage of alpha particles and/or beta particles and/or gamma rays and/or other emission types.
The photon detecting means may be moveable and/or portable.
The detecting means may be mounted on a moveable unit on which they are provided. The moveable unit may be remote controlled, for instance in terms of its position.
The detecting means may be mounted on an inclinable and/or rotatable element. The detecting means may be mounted on a pan and tilt style mounting. The detector means may be remotely controlled, for instance in terms of its inclination or angular position.
The detecting means may be hand-held.
The instrument may comprise a moving belt or other form of transport means. The transport means may be used to move item(s) and/or material to be monitored past the detecting means.
The instrument may comprise a moveable element carrying one or more detecting means. The moveable element may be provided in one configuration to allow monitoring.
The instrument may comprise one or more detecting means provided in a fixed position relative to the area to be monitored. The detecting means may be provided above the area to be monitored. The detecting means may be provided within an item having an area to be monitored, for instance inside a pipe.
The photon detection means may comprise a light sensitive device, such as a photomultiplier. The light sensitive device may be collimated.
The photon detecting means may be selective to a certain wavelengths as detailed in the first aspect of the invention, and/or elsewhere in this document. Preferably the selective waveband is one not containing a significant number of photons under the ambient light conditions for the area. The ambient light may be daylight and/or artificial light. Light may substantially or completely be excluded from the area, for instance, by the instrument.
The instrument may include a range finder, preferably to indicate the distance between the detector and one or more locations within the environment, particularly within the field of view of the detector.
The detecting means may be connected to the processing means directly, for instance through wire(s), or may be indirectly connected, for instance via a radio transmitter.
Preferably the instrument measures emission level. Preferably the instrument measures the position of the source of the signals, for instance as three dimensional co-ordinates.
The instrument may monitor, for instance in relation to alpha emissions, the emissions in terms of one or more of, the total emission level, the emission level of distinct sources and/or areas, the direction of the emission source(s), the distance of the emission source(s) from the detector(s), the position of the emission source(s) relative to the detector(s) and/or relative to the environment the source(s) is in, such as the boundaries of a room.
The indication may express the level of one or more, and preferably each, discrete source found within the environment monitored or areas thereof. The indication may express the overall contamination level of the environment monitored or areas thereof.
The position may be expressed as three-dimensional co-ordinates relative to the environment the source(s) are in. The co-ordinates may be referenced relative to a corner of the environment, such as a corner between floor and two walls. The position may be expressed as an angle, more preferably 2 angles, relative to the detector and a distance between the detector and the source(s).
Positional and level information may be combined in the indication. The indication may comprise one or more 2-D slices or views and/or 3-D representations of the environment or areas thereof together with alpha level indications. Contour plots of the contamination may be provided.